Thomas took bronze in Tokyo and silver in last year’s world championships, but she was in control throughout the final, coming home in 21.83 seconds.
She was in control throughout the final, coming home in 21.83 seconds and breaking into a wide smile of disbelief, hands on her head, when she crossed the finish line.
Alfred, who claimed Saint Lucia’s first Olympic medal when she won the 100m on Saturday, was fastest out of the blocks but was a clear second in 22.08, with Brittany Brown taking bronze for the U.S. in 20.20.
"I'm tired. Long five days," Alfred told reporters. "I did feel ready for the 200m tonight. I feel good, no complaints at all. This means a lot. First Olympics, to go back with gold and silver, I can't ask for more than that."
Thomas arrived in Paris with the world's fastest time this season of 21.78 and made an emphatic statement in Monday's semi-finals when she pulled away from the field with ease over the final 50m to cross the line smiling in 21.86 seconds.
There was more frustration for British duo Dina Asher-Smith and Daryll Neita who finished fourth and fifth.
Jamaica's reigning world champion Shericka Jackson withdrew from Sunday's heats due to injury.
